Adjustable advance limiter for ignition systems



R. R. HILL.

March 4, 1969 ADJUSTABLE ADVANCE LIMITER FOR IGNITION SYSTEMS Filed Dec. '21, 1967 REST/H6750 ADI/4N0.

INVENTOR. RAYMOND 06m H/LL BY I 7z g% f4 ATTORNEYS United States Patent 2 Claims ABSTRACT OF THE DISCLOSURE An advance limiter for conventional automotive ignition systems which essentially comprises a fiat plate with threaded brackets for receiving an adjustment screw, said plate being mounted to the distributor for regulation of the maximum advance developed by the governor.

The present invention relates to a device which will provide an adjustable limitation to spark advancement in conventional ignition systems for automobiles and the like.

Ignition systems as they presently exist for most automobiles have a means in the distributor for setting initial spark advance. In a piston-type, internal combustion engine the firing of a spark plug igniting the combustibles in the compression chamber must be timed to a particular instant in the pistons cycle. The initial setting fixes the firing at a point in the cycle which is proper only at start or cranking speeds. As the speed or r.p.m. is increased, the firing of the spark plug must be advanced for maximum ignition of the combustibles in the compression chamber. This advancement of ignition spark in relation to the increase in r.p.m. of the engine is in general automatically controlled by a conventional centrifugal governor in the distributor. Governor-weights, restrained by springs, act on a cam, which regulates a circuit breaker, to advance the cams rotation in relation to the engine cycle. However, there reaches a point at which advance is at an optimum. To increase the advance beyond this point would cause loss of power from the premature firing of the combustion chamber.

Present distributors have a maximum advance inherent in their construction. However, this position is fixed in relation to the initial setting. Thus, a change in initial setting may produce an undesirable dependant change in maximum setting. Additionally, when the springs are replaced or changed, or the weight of the governor is altered, or a custom camshaft is installed, the requirements of the ignition system are changed and the fixed settings of conventional distributors become inadequate.

The object of my invention is therefore to provide an inexpensive device that can be simply adapted to conventional automobile distributors to provide for manual adjustment of the maximum spark advancement independent of initial spark setting.

It is a further object of my invention to permit easy and quick adjustment in the limitation to spark advancement for changes in engine equipment or operating conditions.

FIG. 1 is a perspective view of the novel advance limiter mounted on a conventional distributor;

FIG. 2 is an enlarged side elevational view in section of the advance limiter and the distributor taken along the line indicated by 2-2 in FIG. 1;

FIG. 3 is an isometric view of the advance limiter showing its relationship to the advance governor and to the stationary portion of the distributor.

Referring now in detail to the drawings, FIG. 1 illustrates the rotating portion of a distributor on which is mounted the advance limiter 12. In a conventional distributor there are essentially four principal mechanical parts: a rotating shaft 14; a points cam 16; an advance "ice governor 18, illustrated in FIG. 3; and a stationary points mount 20, also shown in FIG. 3.

Turning more particularly to FIG. 3, one end of the shaft 14 has a spiral gear (not shown) which connects the rotational output of the engine to the shaft 14. The opposite end mechanically engages a conventional advance governor 18 which advances the rotation of the points cam 16 in relation to the rate of rotation of the shaft 14. The points cam 16 is mounted on a sleeve 22 which fits over the shaft 14. The other end of the sleeve 22 has a plate 24 afiixed in a plane perpendicular to the axis of the sleeve 22. The plate 24 forms a mount for the advance governor 18 and a dielectric distributor cap 26 shown in FIG. 1. The points cam 16 acts upon a pair of electrical contacts 28 initiating an intermittent breaking of an electrical circuit for firing the spark plugs of the engine.

The advance governor 18 functions by maintaining a position of equilibrium for any given rate of rotation by equating the centrifugal force created by two weights 30 with the opposing force of two springs 32. Because of the peculiar shape of the advance governor weights 30 and the end 14' of the shaft 14, a specific advancement of the points cam 16 over the shaft is maintained for a particular r.p.m. of the engine. One of the pins 34 securing a spring 32 to the shaft end 14' extends through a slot 36, in the sleeve plate 24. The purpose of this arrangement is to provide a fixed maximum beyond which the points cam 16 and distributor cap 26 will not advance.

My invention permits this normal maximum advance to be restricted. The advance limiter 12 essentially provides a variable stop for the pin 34 that extends through the slot 36 in the sleeve plate 24. My adjustable advance limiter 12 comprises a flat plate 38 of substantially semiannular shape, which can be attached to the sleeve plate 24 by bolts 40 through the same holes that were provided for the attachment of the distributor cap 26 to the sleeve plate 24. At one end of the fiat plate 38, two extensions are bent perpendicular to the plane of the plate to form a bracket 42 through which an adjustment screw 44 is threaded. The adjustment screw 44 has an enlarged head 44' of suflicient diameter as to interfere with the movement of the pin 34' when moving in the slot 36 as indicated by the phantom lines of the pin in FIG. 2 illustrating its most advanced position. The graphical illustration at the top of FIG. 3 indicates one position to which the normal advance may be limited to a restricted advance when further movement of the pin 34 is prevented by the enlarged head 44' of the adjustment screw 44. The advance limiter 12 and the distributor cap 26 are bolted to the sleeve plate 24 as illustrated in FIG. 1. To facilitate adaption of the advance limiter 12, a special nut 46 with a cross groove may be used to permit use of a screwdriver in the confined access on the distributor cap 26.

To prevent any movement of the adjustment screw caused by vibration, a small semiresilient button 48 may be inserted between the plate and adjustment screw. It has been found that nylon makes a suitable material for this purpose. After removal of the outer cover of the distributor (not here shown), only a screwdriver is required to adjust the setting on the advance limiter 12.

The foregoing drawings and specification describe one embodiment of my invention. Modifications in the disclosed invention may be made without departing from the spirit and scope of my invention. In some instances when the advance limiter 12 is adapted to a conventional distributor of design different than that herein described, modification may be essential to permit proper functioning of the adjustable advance limiter invented.

I claim:

1. In an automotive ignition system having an ignition points cam with a sleeve plate attached thereto for rotation therewith, a rotary plate adapted to be connected to the cam shaft of an engine and rotated thereby at a speed proportional to the operational speed of the engine, a pair of centrifugally operated weights interconnecting said sleeve plate and said rotary plate through an advancement angle which is proportional to the operating speed of said engine, a pin mounted on said rotary plate and extending through an enlarged aperture in said sleeve plate, and a pair of apertures in said sleeve plate adapted to receive mounting bolts for a cover, the improved advance limiter which comprises:

(A) a substantially semiannular plate having a central opening accessible from one edge of said plate and a pair of mounting holes at opposite ends of said plate with said mounting holes positioned in alignment with said apertures in said sleeve plate, (B) a pair of upstanding ears on said semiannular plate,

and (C) a threaded screw extending through both and threadedly engaged with at least one of said upstanding ears with the axis of said screw extending adjacent to said pin and with said screw having an enlarged head portion engageable with the side of said pin for limiting said advance angle.

2. The improved advance limiter of claim 1 characterized further by the inclusion of a resilient pad mounted on said semiannular plate between said upstanding ears engaging the threads of said screw for preventing vibrational movement of said screw.

References Cited UNITED STATES PATENTS 1,590,772 6/1926 Moore 6425 15 2,699,657 1/1955 Vogel 64-25 3,196,224 7/ 1965 Tagliabue 20022 LAURENCE M. GOODRIDGE, Primary Examiner.

US. Cl. XR 

